Vehicle seat

ABSTRACT

A vehicle seat is composed of: a base member  40  elastically connected to and supported on any of frame members arranged separately in a width direction of a seat frame, through metal springs  41,  to constitute a lower layer; a first net member  50  of a three-dimensional structure, in which a front mesh layer and a back mesh layer are connected by a large number of piles, stretched above the base member  40  and between the frame members arranged separately in the width direction, to constitute a middle layer; and a second net member  60  of a three-dimensional structure, in which a front mesh layer and a back mesh layer are connected by a large number of piles, disposed to cover the top of the middle layer and stretched with a tension lower than that of the first net member constituting the middle layer, to constitute an upper layer.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a vehicle seat for a car or thelike.

[0002] In recent years, a known vehicle seat uses a net member of athree-dimensional structure which can provide a high cushioning abilityeven if it is a thin type and is excellent in air permeability becauseof a large number of air gaps as compared with a pad member such asurethane or the like. Its front mesh layer and back mesh layer areconnected by a large number of piles to form a truss structure(three-dimensional structure), which is an elastic structure withresistance to settling and is excellent in air permeability, bodypressure dispersion characteristics, impact absorbing characteristicsand the like.

[0003] Though the vehicle seat using the net member of athree-dimensional structure has the above-described excellentcharacteristics, providing body pressure dispersion characteristics andimpact absorbing characteristics at higher levels is always required.Further, it is also required to support the body of a seated person asstably as possible because if the seated person's body moves up and downdue to vibrations or the like during driving, the above characteristicscan not be exhibited effectively. Furthermore, since the net member of athree-dimensional structure can exhibit a cushioning ability, impactabsorbing characteristics and the like at high levels as describedabove, one with a thin-profile can be used as compared with the padmember such as urethane or the like, but it is desired to decrease thefeeling of touch with its seat frame to the minimum in order to improvethe feeling of seating.

SUMMARY OF THE INVENTION

[0004] The present invention is made in view of the above-describedcircumstances and its object is to provide a vehicle seat capable ofproviding body pressure dispersion characteristics, impact absorbingcharacteristics and the like at levels higher than those of theconventional case. Further, another object is to provide a vehicle seatwhich can decrease the feeling of touch with its seat frame.

[0005] In order to attain the above objects, a vehicle seat inaccordance with one aspect of the present invention is characterized byhaving a base member elastically connected to and supported on any offrame members arranged separately in a width direction of a seat frame,through metal springs, to constitute a lower layer; a first net memberof a three-dimensional structure, in which a front mesh layer and a backmesh layer are connected by a large number of piles, stretched above thebase member and between the frame members arranged separately in thewidth direction, to constitute a middle layer; and a second net memberof a three-dimensional structure, in which a front mesh layer and a backmesh layer are connected by a large number of piles, disposed to coverthe top of the middle layer and stretched with a tension lower than thatof the first net member constituting the middle layer, to constitute anupper layer.

[0006] The vehicle seat in another aspect of the present invention ischaracterized in that the base member is located between frame membersconstituting a seat cushion part which are arranged separately in thewidth direction of the seat frame, and the metal spring runs betweeneach frame member and each side portion of the base member.

[0007] The vehicle seat in another aspect of the present invention ischaracterized in that the base member is further elastically supportedhung through a metal spring engaged with any of frame membersconstituting a seat back part of the seat frame.

[0008] The vehicle seat in another aspect of the present invention ischaracterized in that the base member is connected to means forpreventing bounce upward.

[0009] The vehicle seat in another aspect of the present invention ischaracterized in that the base member is a substantially flat-typeelastic member.

[0010] The vehicle seat in another aspect of the present invention ischaracterized in that the substantially flat-type elastic memberconstituting the base member is a net member of a three-dimensionalstructure in which a front mesh layer and a back mesh layer areconnected by a large number of piles.

[0011] The vehicle seat in another aspect of the present invention ischaracterized in that the first net member constituting the middle layeris stretched in loop form between the frame members arranged separatelyin the width direction.

[0012] The vehicle seat in another aspect of the present invention ischaracterized in that a viscoelastic member is inserted between a partof the first net member constituting the middle layer covering the framemember and the second net member constituting the upper layer, orbetween the first net member constituting the middle layer and the framemember around which the first net member is wound.

[0013] The vehicle seat in another aspect of the present invention ischaracterized in that the viscoelastic member is formed into a structurehaving a plurality of divided block parts with one or more boundaryparts, which are processed thin in thickness, intervening therebetween.

[0014] The vehicle seat in another aspect of the present invention ischaracterized in that the viscoelastic member is formed includingviscoelastic polyurethane, or is formed including a net member of athree-dimensional structure, in which a front mesh layer and a back meshlayer are connected by a large number of piles, formed into a structurehaving a plurality of divided block parts with one or more boundaryparts, which are processed thin in thickness, intervening therebetween.

[0015] The vehicle seat in another aspect of the present invention ischaracterized in that the viscoelastic member is formed including a netmember of a three-dimensional structure, in which a front mesh layer anda back mesh layer are connected by a large number of piles, formed intoa structure having a plurality of divided block parts with one or moreboundary parts, which are processed thin in thickness, interveningtherebetween, and viscoelastic polyurethane which is integrally joinedto one face of the net member of a three-dimensional structure.

[0016] The vehicle seat in another aspect of the present invention ischaracterized in that the viscoelastic member is formed including a netmember of a three-dimensional structure, in which a front mesh layer anda back mesh layer are connected by a large number of piles, formed intoa structure having a plurality of divided block parts with one or moreboundary parts, which are processed thin in thickness, interveningtherebetween, and an elastic base member to either face of which the netmember of a three-dimensional structure is integrally joined.

[0017] The vehicle seat in another aspect of the present invention ischaracterized in that a viscoelastic member which is connected to andsupported on any of the frame members forming the seat frame is furtherdisposed at one or both of a front edge portion of the seat cushion partand a lumbar supporting part and below the second net member forming theupper layer.

[0018] The vehicle seat in another aspect of the present invention ischaracterized in that only one end of the viscoelastic member disposedon the front edge portion of the seat cushion part is connected to andsupported on any of the frame members disposed at the front end of theseat frame for the seat cushion part.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a partially cross-sectional view showing a schematicstructure of a vehicle seat according to one embodiment of the presentinvention;

[0020]FIG. 2 is a perspective view for explaining a seat frame of thevehicle seat according to the above embodiment;

[0021]FIG. 3 is a cross-sectional view for explaining a structure of anaspect of a seat cushion part of the vehicle seat according to the aboveembodiment;

[0022]FIG. 4 is a cross-sectional view for explaining a structure ofanother aspect of the seat cushion part of the vehicle seat according tothe above embodiment;

[0023]FIG. 5 is a cross-sectional view for explaining a structure of aseat back part of the vehicle seat according to the above embodiment;

[0024]FIG. 6 is a perspective view for explaining a base memberconstituting the seat cushion part and a back lining net memberconstituting the seat back part of the vehicle seat according to theabove embodiment;

[0025]FIG. 7A is an enlarged view of A part in FIG. 6 and FIG. 7B is aview showing an aspect in which an iron plate is interposed;

[0026]FIG. 8 is an enlarged view of C part in FIG. 6;

[0027]FIG. 9 is an enlarged view of B part in FIG. 6;

[0028]FIGS. 10A to 10C are views for explaining structures of aviscoelastic member;

[0029]FIG. 11 is a view for explaining a structure in which theviscoelastic member is disposed at a lumbar supporting part;

[0030]FIG. 12 is a cross-sectional view showing a part of a net memberof a three-dimensional structure used in the above-described embodiment;

[0031]FIG. 13 is an enlarged view showing a front mesh layer of the netmember shown in FIG. 12;

[0032]FIG. 14 is an enlarged view showing a back mesh layer of the netmember shown in FIG. 12;

[0033]FIGS. 15A to 15E are views for explaining manners of arrangingpiles;

[0034]FIG. 16 is a perspective view for explaining another embodiment ofthe base member;

[0035]FIG. 17 is a perspective view for explaining another embodiment ofthe base member;

[0036]FIG. 18 is a perspective view for explaining another embodiment ofthe base member;

[0037]FIG. 19 is a perspective view for explaining another embodiment ofthe base member;

[0038]FIG. 20 is a perspective view for explaining another embodiment ofthe base member;

[0039]FIG. 21A is a graph of load-deflection curved lines showing staticcharacteristics when a load is applied using a compressed plate in theshape of the haunches, and FIG. 21B is a view for explaining components;

[0040]FIG. 22 is a view showing measured results of vibrationtransmissibility;

[0041]FIGS. 23A and 23B are views for explaining vibration absorbingcharacteristics of the seat cushion part;

[0042]FIGS. 24A and 24B are views for explaining vibration absorbingcharacteristics of the seat back part and the seat cushion part in anembodiment 1;

[0043]FIGS. 25A and 25B are views for explaining vibration absorbingcharacteristics of the seat back part and the seat cushion part of anurethane seat that is a comparative example 4;

[0044]FIG. 26 is a view showing data of the embodiment 1 in FIG. 24through the relation between cycle and acceleration;

[0045]FIG. 27 is a view showing data of the comparative example 4 inFIG. 25 through the relation between cycle and acceleration;

[0046]FIG. 28 is a graph showing results of vibration characteristicsinvestigated by vibrating a seat by means of a vibrator based on randomwaves taken on Chugoku Expressway and mounting an accelerometer on thehead of a test subject; and

[0047]FIG. 29 a graph showing results of the same experiment as in thecase of FIG. 28 which was carried out based on random waves taken onMetropolitan Expressway.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] Hereinafter, the present invention is explained in more detailbased on the embodiments shown in the drawings. First, referring to FIG.1 to FIG. 11, the structure of a vehicle seat 10 according to theembodiment is explained. As shown in FIG. 1, the vehicle seat 10comprises a seat frame 20, a base member 40, a first net member 50, anda second net member 60.

[0049] The seat frame 20, as shown in FIG. 2, comprises a cushion mainframe 21 for forming a seat cushion part and a back main frame 22 forforming a seat back part. Each of them is composed of a frame member inthe form of pipe, and this frame member of the cushion main frame 21 isbent into substantially the shape of the letter U so that its closedside is disposed at the front. The frame member of the back main frame22 is bent into a substantially square shape and to form a headsupporting frame part 22 d with a small width at the top.

[0050] Base ends of the cushion main frame 21 are connected, with bolts24 a, to slide frames 24 which slide along rail members 23 disposed atthe floor of a vehicle. Further, middle parts of side frame members 21 aand 21 b, which are provided at positions separated from each other inthe width direction of the cushion main frame 21, are also connected tothe slide frames 24 with first brackets 25 and bolts 25 a. Accordingly,the cushion main frame 21 is provided to be slidable along the railmembers 23.

[0051] At the rear ends of the slide frames 24, second brackets 27 areprovided to be rotatable through a shaft 26, and third brackets 28 whichare provided at the bottom ends of the back main frame 22 are connectedfixedly to the second brackets 27. Numeral 29 denotes a reclining dial,and rotation of the reclining dial 29 causes the back main frame 22 torecline back and forth with respect to the cushion main frame 21.

[0052] Below each of the side frame members 21 a and 21 b of the cushionmain frame 21, provided are a first auxiliary frame member 30 and asecond auxiliary frame member 31 whose base ends are fixed to the slideframe 24 respectively and the other end of the former is fixed to thefirst bracket 25 and the other end of the latter is fixed to a front endframe member 21 c of the cushion main frame 21. Further, each endportion of a third auxiliary frame member 32 which is formed insubstantially the shape of the letter U is fixed to the front end framemember 21 c.

[0053] Further, auxiliary frame members 33 and 34 are provided to belocated behind each of the side frame members 22 a and 22 b of the backmain frame 22 and inside either the side frame members 22 a or 22 bviewed from the front.

[0054] The base member 40 which is disposed below the first net member50 and the second net member 60 and constitutes a lower layer iselastically connected to and supported on, through metal springs 41, anyof the frame members which are disposed separately from each other inthe width direction from among the frame members constituting the seatcushion part. In this embodiment, as shown in FIG. 3, FIG. 4 and FIG. 6,ends of the metal springs 41 are disposed to be engaged with the firstauxiliary frame members 30 and 30 disposed below the side frame members21 a and 21 b respectively, and a rim portion of the base member 40 isengaged with the other ends thereof, thereby stretching the base member40 between the first auxiliary frame members 30 and 30 which aredisposed separately in the width direction. Further, the front end ofthe base member 40 is supported on the third auxiliary frame member 32which is fixed to the front end frame member 21 c of the cushion mainframe 21.

[0055] The reason why the base member 40 is elastically connected andsupported through the metal springs 41 as described above is that thebase member 40 is stroked by vibrations to absorb vibrations transmittedto the first net member 50 and the second net member 60 disposed atupper layers utilizing phase delay. The material forming the base member40 is not limited, but it is preferable that, in addition to absorptionof vibrations by strokes of the metal springs 41, the base member 40itself is a substantially flat-type elastic member which absorbsvibrations and hardly transmits them. As the above-described base member40, for example, a so-called Pullmaflex can be used in which wires areformed in reed screen form or in net form, but it is preferable to usethe same net member of a three-dimensional structure as that of thefirst net member 50 and the second net member 60 described below. Asshown in FIG. 7A, when the net member of a three-dimensional structureis used, a plastic plate 42 is secured to one surface of a rim portion40 a by vibration welding, and the other end of the metal spring 41penetrates through the plastic plate 42 for engagement. In order toprevent the rim portion 40 a from being damaged by pull due to pressureexerted on the surface, it is also possible to interpose an iron piece43 between the rim portion 40 a and the plastic plate 42 as shown inFIG. 7B. In place of the plastic plate 42, a metallic wire can beinserted.

[0056] The first net member 50 is disposed above the base member 40 toconstitute a middle layer. The first net member 50 is stretched betweenany frame members, which are disposed separately in the width direction,of the seat frame 20 constituting the seat cushion part with a tensionhigher than that of the second net member 60 described below whenstretched. In the embodiment, as shown in FIG. 3 and FIG. 4, it isstretched between the side frame members 21 a and 21 b of the seat frame20 which are located above the first auxiliary frame members 30 and 30stretching the aforementioned base member 40 therebetween. The framemembers applicable for the stretch are not limited to the side framemembers 21 a and 21 b constituting the side frame 21, but the stretchcan also be made between separately provided auxiliary frame members(not shown). However, the first net member 50 is spread between the sideframe members 21 a and 21 b, whereby the surfaces of the side framemembers 21 a and 21 b are also covered with the first net member 50,which serves to decrease the feeling of touch with the side framemembers 21 a and 21 b.

[0057] The reason why the first net member 50 is stretched with a hightension as described above is that when a person sits on the second netmember 60 which is disposed thereabove, the first net member 50 providesa feeling of stiffness by its reaction force to stably hold the seatedperson. Further, the first net member 50 is connected to theaforementioned base member 40 so as to increase face stiffness of thelower part to cope with deformation of the upper part while the basemember 40, which is stretched 25 between the first auxiliary framemembers 30 and 30 through the metal springs 41, exhibits high vibrationabsorbency, resultingly providing a feeling of stiffness to improve thefeeling of seating.

[0058] Means for stretching the first net member 50 between the sideframe members 21 a and 21 b is optional. Though the first net member 50can be stretched in plate shape by winding its rim portion around theside frame members 21 a and 21 b, it is preferable to stretch it in loopshape between the side frame members 21 a and 21 b as shown in FIG. 3and FIG. 4. When the first net member 50 is formed in loop shape and thebase member 40 is connected to a part 50 a located at the lower side,the second net member 60 is disposed on a part 50 b located at the upperside, so that transmission of vibrations to the second net member 60 isdecreased as compared with the case where the first member 50 isstretched in plate shape to be connected to the base member 40. Further,a space which is formed between the part 50 a located at the lower sideand the part 50 b located at the upper side can provide a feeling ofstroke. Furthermore, because of the loop shape, characteristics of thenet can be utilized in the three dimensions to make it possible todesign four spring constants (selection of characteristic of the part 50b located at the upper side or the first net member 50, selection ofcharacteristic of a connecting net 53 described below, selection ofcharacteristics of the first net member 50 and the connecting net 53 inaccordance with magnitude of load, metal spring characteristic) bycompression (buckling) characteristics, tensile characteristics, andmetal spring characteristics, whereby linearity can be reinforced, andamplitude, frequency, or transfer function independent from load masscan be designed.

[0059] Though a connecting means between the first net member 50 and thebase member 40 is optional, they are connected in this embodiment byfixing substantially U-shaped plates 52 and 42 to the back face of thepart 50 a, which is located at the lower side of the first net member 50stretched in loop shape, and to the top face of the base member 40respectively with the plates 52 and 42 disposed in opposite directionsto each other, and engaging both plates 52 and 42. Means for fixing theU-shaped plates 52 and 42 to the first net member 50 or the base member40 is optional, and, for example, small holes are provided in the plates52 and 42, making it possible to fix them by sewing even if the plates52 and 42 are made of plastic or metal. Further, in the case of plastic,a vibration welding means can be employed.

[0060] To stretch the first net member 50 in loop shape between the sideframe members 21 a and 21 b, as shown in FIG. 4, the first net member 50is previously formed to have a length to the extent that its edges 50 cand 50 d overlap when it is wound around the side frame members 21 a and21 b to be formed in loop shape, and the overlapping edges 50 c and 50 dare fixed to each other. Fixing means in this event may be a vibrationwelding means or a sewing means. In the case of sewing, they can besewed together with the aforementioned substantially U-shaped plate 52.

[0061] Further, as the aspect shown in FIG. 3, it is also possible thatthe first net member 50 is formed to have a length shorter than that ofthe above-described aspect shown in FIG. 4, and the connecting net 53 isprovided between the edges 50 c and 50 d by the vibration welding meansor the sewing means. The connecting net 53 is provided to be located atthe lower side when the first net member 50 is stretched in loop shapebetween the side frame members 21 a and 21 b. Since the connecting net53 does not perform a function of supporting a load but is used tostretch the first net member 50 with a high tension, a functionnecessary to support a load is not essential for it, and thus aconnecting net with a relatively low elasticity is used therefor.

[0062] The second net member 60 is disposed above the first net member50 to constitute the upper layer. The second net member 60 is providedwith trim cloths 61 and 62 at the ends. In the aspect shown in FIG. 4A,the trim cloths 61 and 62 are passed around the peripheral faces of thefirst net member 50 which are disposed around the side frame members 21a and 21 b, further wound around the first auxiliary frame members 30and 30 disposed below the side frame members 21 a and 21 b to be foldedinward, and sewed to the base member 40, thereby stretching the secondnet ember 60 between the side frame members 21 a and 21 b. The tensileforce in this case is set to be lower than that of the first net member50, so that when a person sits thereon, the second net member 60 bendsalong the shape of the human body to contact with the first net member50. Accordingly, the second net member 60 and the first net member 50exhibit their own body weight pressure dispersion characteristics andvibration absorbing characteristics. The first net member 50 isstretched with a high tension to prevent unintended sinking and supportthe second net member 60, whereby a feeling of stiffness of the firstnet member 50 is transmitted through the second net member 60 to theseated person. Further, the second net member 60 is loosely stretched,which does not interfere with the mechanism of absorbing vibrations bymeans of the metal springs 41, the base member 40, the first net member50 and the connecting net 53. If the second net member 60 is tightlystretched, movements of the connecting net 53 and the metal springs 41are suppressed, making it difficult to generate movement by resilienceof the metal springs 41. More specifically, the second net member 60 andthe first net member 50 are necessarily set in the stretching way asdescribed above not to prevent such movements that the metal springs 41do not actively work in a static seating condition but function withphase delay when an impact vibration or a force due to a greatdisplacement exerts thereon.

[0063] The stretching means for the second net member 60 is not limitedto the above-described means, but the second net member 60 can bestretched, as shown in FIG. 3, by means such as sewing of the ends ofthe trim cloths 61 and 62, together with the base member 40, to theplates 42 fixed to the base member 40.

[0064] Further, it is preferable to dispose viscoelastic members 70, asshown in the drawings, between the first net member 50 and the secondnet member 60 and close to the side frame members 21 a and 21 brespectively. The provision of the viscoelastic members 70 makes itpossible to absorb vibrations transmitted along the side frame members21 a and 21 b also by the viscoelastic members 70, and decrease thefeeling of touch with the side frame members 21 a and 21 b, resulting inimproved feeling of support of femurs. When a rim portion 60 a of thesecond net member 60 is disposed to be inserted between the viscoelasticmember 70 and the second net member 50 as shown in FIG. 4B, the feelingof touch with each of the side frame members 21 a and 21 b can bedecreased more.

[0065] Viscoelastic polyurethane can be used as the viscoelastic member70. The viscoelastic member 70 which is processed into substantiallycylindrical form can be used as it is. However, in order to impart aproperty of keeping shape by resilience and face stiffness to theviscoelastic material with high damping property, it is preferable toform at predetermined intervals a boundary part 70 a which is processedto become smaller in thickness and form block parts 70 b and 70 b eachhaving a shape whose middle portion bulges out as shown in FIG. 10A. Inthe case of the structure composed of viscoelastic polyurethane,however, a heat welding means is used to form the boundary part 70 a, inwhich the size and shape of the block parts 70 b and 70 b can be changedthrough setting of the number of formation, width and the like of theboundary parts 70 a to arbitrarily adjust the face stiffness.

[0066] Further, as the viscoelastic member 70 with a high contributionratio to damping characteristics, it is preferable to use a viscoelasticmember made by integrally joining viscoelastic polyurethane 71 and a netmember of a three-dimensional structure 72 as shown in FIG. 10B in orderto impart a spring property thereto in a direction perpendicular to ahuman body to improve vibration absorbency. Also in this case, it ispreferable that the viscoelastic polyurethane 71 and the net member of athree-dimensional structure 72 are respectively formed with boundaryparts 71 a and 72 a, which are processed to become smaller in thickness,to be in shapes having block parts 71 b and 72 b which bulge out withthe boundary parts 71 a and 72 a as boundaries.

[0067] Further, in order to make the viscoelastic member 70 at lowercost, different kinds of elastic members which are available at lowprices are combined to make the viscoelastic member 70 which has bothspring characteristics and damping characteristics as shown in across-sectional view of FIG. 10C. The viscoelastic member 70 shown inFIG. 10C is made by integrally joining net layers 74 and 75, which areeach composed of a net member of a three-dimensional structure as shownin FIG. 12 to FIG. 15, to both surfaces of an elastic base member 73disposed therebetween.

[0068] As the elastic base member 73, it is preferable to use foamedpolyurethane which is formed in an appropriate thickness. The net layers74 and 75 joined to both surfaces of the elastic base member 73 areformed with boundary parts 74 a and 75 a respectively at predeterminedintervals and with block parts 74 b and 75 b with the boundary parts 74a and 75 b as boundaries.

[0069] Incidentally, means for forming the boundary parts 74 a and 75 aare optional. For example, means for sewing can be suggested in whichafter net members constituting the net layers 74 and 75 are layered onthe elastic base member 73, sewing is performed from one net layer 74through the elastic base member 73 to the other net layer 75 along partscorresponding to the boundary parts 74 a and 75 a. Further it is alsopossible that after the net members constituting the net layers 74 and75 are layered on the elastic base member 73, they are sandwichedbetween protruding parts of dies for vibration welding (not shown) tointegrally join those three members by vibration welding. Further, it isalso possible that a net member of a three-dimensional structure whichis reinforced in buckling characteristics is used for the viscoelasticmember 70 to provide pseudo-viscoelastic characteristics only from thenet member of a three-dimensional structure. For example, it is possibleto make a structure in which the net member of a three-dimensionalstructure in the form of an entirely flat plate is used as theabove-described elastic base member 73, and the aforementioned netlayers 74 and 75 are layered on both sides thereof. Furthermore, it isalso possible to make a structure in which the above net layers 74 and75 are directly layered without the elastic base member 73 intervening.

[0070] It is preferable to securely dispose the viscoelastic member 70with one end thereof sandwiched also between the front end frame member21 c which is disposed at the front end of the substantially U-shapedcushion main frame 21 of the seat cushion part and the above-describedsecond net member 60 as shown in FIG. 1 and FIG. 11. In this case, it ispreferable to secure only one end of the viscoelastic member 70 to thefront end frame member 21 c and dispose the other end 70 c as a free endin a space between the second net member 60 and the base member 40.

[0071] Vibrations transmitted through the front end frame member 21 c ofthe cushion main frame 21 a re absorbed by the viscoelastic member 70which is connected to and supported on the front end frame member 21 c,thereby suppressing transmission of vibrations to the second net member60. Further, the other end of the viscoelastic member 70 is kept to be afree end, thereby making it easier for absorbed vibration energy todisperse and easing rapid change in section modulus, which results indecreased feeling of foreign matter caused by the viscoelastic member 70itself. Further, since the positions of back of thighs of the seatedperson are raised by the thickness of the viscoelastic member 70, thestability during seating is improved and the feeling of touch with thefront end frame member 21 c of the side frame 21 is decreased,preventing the haunches from slipping due to turn of the pelvis of theseated person.

[0072] As the viscoelastic member 70 which is connected to and supportedon the front end frame member 21 c, any of viscoelastic polyurethane, amember made by layering the viscoelastic polyurethane 71 and the netmember of a three-dimensional structure 72, and a member made byintegrally joining the net layers 74 and 75 on both surfaces of theelastic base member 73 can be used similarly to the viscoelastic member70 mounted on the side frame members 21 a and 21 b. Moreover, it ispreferable that boundary parts are formed in the above members toprovide a structure having a plurality blocks in order to impartpredetermined face stiffness thereto, which is also the same as theabove description.

[0073] It is preferable to dispose farther the viscoelastic member 70also at a lumbar supporting part as shown in FIG. 11. The lumbarsupporting part is provided close to the bottom of the side framemembers 22 a and 22 b of the back main frame 22 constituting the seatback part, that is, in the vicinity of a lower frame member 22 c. Theusable material and structure for the viscoelastic member 70 arecompletely the same as those of the above-described case, and, forexample, as shown in FIG. 11, a member having a form which is divided inthree block parts can be used.

[0074] The viscoelastic member 70 as described above is provided at thelumbar supporting part, whereby vibrations transmitted through the sideframe members 22 a and 22 b and the lower frame member 22 c of the backmain frame 22 can be absorbed. Further, the lumbar supporting part ofthe seat back part decreases reaction force by the viscoelastic member70 to bulge out forward along the shape of the human body, resulting inimproved supporting property for the lumbar.

[0075] It should be noted that even if only one of the viscoelasticmember 70 connected to the front end frame member 21 c of the cushionmain frame 21 and the viscoelastic member 70 provided at the lumbarsupporting part is provided, vibration absorbing characteristics and thestability during seating can be improved, but they are preferablyprovided at both positions in order to improve their characteristicsmore.

[0076] As shown in FIG. 6, a back lining net member 80 whose rimportions 81 and 82 are connected to the side frame members 22 a and 22 brespectively is stretched over the back main frame 22. Specifically, asshown in FIG. 9, the rim portions 81 and 82 are wound from the frontside of the side frame members 22 a and 22 b toward the back siderespectively. U-shaped plates 85 which are fixed to the edges of the rimportions 81 and 82 by vibration welding or sewing are engaged withattachment plates 22 e which protrude backward from the side framemembers 22 a and 22 b, thereby stretching the back lining net member 80.A U-shaped plate 83 a is fixed by vibration welding to the edge of alower rim portion 83 of the back lining net member 80, and this U-shapedplate 83 a is engaged with an auxiliary frame member 35 which isdisposed behind the lower frame member 22 c of the back main frame 22.Further, a U-shaped plate not shown is attached by vibration welding tothe edge of an upper rim portion 84 of the back lining net member 80.This U-shaped plate is engaged with an auxiliary frame member 36 whichis disposed behind the back main frame member 22 in the vicinity of theboundary with the head supporting frame part 22 d of the back main frame22.

[0077] The back lining net member 80 is constituted of a net member of athree-dimensional structure and stretched with substantially the samehigh tension as that of the above-described first net member 50 which isstretched over the cushion main frame 21, so that when the load of theseated person exerts on the back lining net member 80 through a skinmember covering it, the back lining net member 80 provides feelings ofspring and stiffness by its resilience to stably hold the seated personand absorb vibrations.

[0078] On the back lining net member 80, as shown in FIG. 6 and FIG. 8,plastic plates 85 and 86 are fixed on the back face side at thepositions corresponding to the lumbar of the person during seating byvibration welding to extend in the lateral direction. Because they arefixed by vibration welding, the opposite faces to the fixed faces of theplates 85 and 86 on the back lining net member 80, that is, the frontfaces, are formed with concave portions 80 a which correspond to theshapes of the plates 85 and 86 as shown in FIG. 8. The concave portions80 a are provided, thereby making it possible to adjust the stretchingdegree of the skin member layered on the back lining net member 80. Morespecifically, when the skin member is stretched over the back main frame22, tension concentrating on the edges is dispersed around the concaveportions 80 a, which makes it possible to partially form parts with highstiffness, thereby providing variations in pressure for supportingattitude and easing touch of the edges of the skin member. Incidentally,the concave portions 80 a can be arbitrarily changed in the number offormation, width, length and the like by the material, thickness and thelike of the net.

[0079] The skin member layered on the back lining net member 80 iscomposed of the net member of a three-dimensional structure similarly tothe above-described second net member 60 which is the skin memberstretched over the cushion main frame 21. This skin member can becomposed of a different member from the above-described second netmember 60 to be stretched over the back main frame 22 in an individualstate. In this embodiment, however, the above-described second netmember 60 is, as shown in FIG. 1, formed into one-piece structure whichserves as both the skin member for the seat cushion part and the skinmember for the seat back part to be stretched thereover. When the skinmember is formed into the one-piece structure as described above, thestiff feeling of touch with the frame member located at the boundarybetween the seat back part and the seat cushion part can be eliminatedto improve the feeling of seating.

[0080] It should be noted that the tension at a part corresponding tothe skin member of the seat back part of the second net member 60 is setto be lower than that of the back lining net member 80. As a result,when a person sits thereon, the part corresponding to the skin member ofthe seat back part of the second net member 60 bends along the shape ofthe human body to contact with the back lining net member 80.Accordingly, the second net member 60 and the back lining net member 80exhibit their own body weight pressure dispersion characteristics andvibration absorbing characteristics. The back lining net member 80 isstretched with a high tension to prevent unintended sinking and supportthe second net member 60, whereby the feeling of stiffness of the backlining net member 80 is transmitted through the second net member 60 tothe seated person, and the second net member 60 is loosely stretched,which does not interfere with the effects of absorbing vibrations bymeans of the back lining net member 80. Further, even when inertialforce is inputted by pitching, yawing, or rolling, the inertial forcecan be absorbed by a follow-up property of the second net member 60having a low surface tension.

[0081] The second net member 60 which is provided at a partcorresponding to the skin member of the seat back part is folded inwardat both rims as shown in FIG. 5 to hold the viscoelastic members 70therein in order to decrease the feeling of touch with the side framemembers 22 a and 22 b. Further, a trim cloth 87 is provided at each rim,and a U-shaped plate 88 attached on the trim cloth 87 is disposed to beengaged with the auxiliary frame member 34, thereby stretching thesecond net member 60.

[0082] Next, the structure of a net member 100 of a three-dimensionalstructure which is employed as the above-described base member 40, firstnet member 50, second net member 60, and back lining net member 80 isexplained with reference to FIG. 12 to FIG. 15. The net member 100 is,as shown in FIG. 12, formed in a solid truss structure(three-dimensional structure) having a front mesh layer 110, a back meshlayer 120, and a large number of piles 130 connecting the front meshlayer 110 and the back mesh layer 120.

[0083] The front mesh layer 110 is formed in a structure having, forexample, a honeycombed (hexagonal) mesh made from multifilamentscomposed of stranded monofilaments, as shown in FIG. 13. The back meshlayer 120 is formed, for example, by rib knitting multifilamentscomposed of stranded monofilaments, as shown in FIG. 14, into astructure having a smaller mesh (fine mesh) than the honeycombed mesh ofthe front mesh layer 110. The pile 130 is formed of monofilaments ormultifilaments which are knitted between the front mesh layer 110 andthe back mesh layer 120 so that the front mesh layer 110 and the backmesh layer 120 maintain a predetermined space therebetween, therebyimparting a predetermined stiffness to the net member 100 which is now asolid mesh knit. Incidentally, when the word “fiber” is simply used inthis description, it means including spun yam or the like as well as amonofilament and a multifilament.

[0084] In addition, though in the above explanation, a layer having ahoneycombed mesh is defined as the front face (for example, a surface ofthe seat cushion part and the seat back part in contact with the humanbody), it is acceptable to use the above layer as the back face, and alayer having a small mesh as the front face. It is naturally acceptableto adopt a mesh shape other than the honeycombed shape or the fine meshshape as the structure of the mesh layer, as shown in Table 1 shownbelow.

[0085] As a material to compose the front mesh layer 110, the back meshlayer 120 or the pile 130, a thermoplastic resin is preferable. Thefollowing resins can be used, for example, thermoplastic polyesterresins such as polyethylene terephthalate (PET) and polybutyleneterephthalate (PBT), polyamide resins such as nylon 6 and nylon 66,polyolefin resins such as polyethylene and polypropylene, or a mixedresin containing two or more kinds of these resins.

[0086] The thickness of a fiber composing the pile 130 should be, forexample, 380 d or more, preferably 600 d or more. As a result, the loadgenerated by the seated person can be supported by deformation of themesh composing the respective mesh layers 110 and 120, and falling andbuckling characteristics of the pile 130, and resilience of the adjacentpiles 130 which impart spring characteristics to the bucklingcharacteristics, that is, it can be supported by the bucklingcharacteristics with resilience, so that the seat can be of a softstructure without concentration of stress.

[0087] Several characteristics of the net member 100 which is suitableto be used as the base member 40, the first net member 50, and thesecond net member 60 are exemplified in Table 1. TABLE 1 NUMBER 1 2 3 45 6 MATERIAL NYLON POLYESTER ← ← ← ← WEIGHT (g/m²) 888 784 864 984 8761128 DENSITY LONGITUDINAL 8.0 7.5 ← 8.5 7.0 8.5 (fibers/inch) LATERAL14.0 13.0 ← ← 14.0 13.0 (fibers/inch) THICKNESS OF FRONT FACE 220d/1f1300d/96f ← ← ← ← FIBER BACK FACE 500d/70f ← ← ← ← PILE 880d/1f 600d/1f← ← 800d/1f ← TENSILE LONGITUDINAL 38.0 156.9 158.4 152.1 148.7 159.3STRENGTH LATERAL 24.8 62.1 79.4 136.5 57.5 130.1 (kg/5 cm) ELONGATION(%) LONGITUDINAL 111.1 56.2 62.5 48.3 50.1 50.2 LATERAL 189.3 66.4 68.243.3 78.0 40.0 TEAR STRENGTH LONGITUDINAL 33.8 87.9 79.2 75.0 91.1 77.7(kg) LATERAL 26.2 49.2 44.9 63.7 41.1 66.7 DISTORTION LONGITUDINAL — 2.6← 2.7 1.4 1.2 RATIO BY LATERAL — 10.6 2.7 5.6 4.6 0.2 REPEATED LOADINGABRASION LONGITUDINAL — 4.5 ← ← ← ← RESISTANCE LATERAL — 4.0 ← 4.5 ← ←MESH LAYER FRONT MESH HONEY ← MESH HONEY MESH STRUCTURE COMB COMB BACKMESH FINE ← FINE FINE FINE MESH MESH MESH MESH PILE STRUCTURE PARALLELCROSS PARALLEL CROSS PARALLEL CROSS

[0088] In Table 1, “d” indicates “denier” and “1 d” is a unit ofthickness when one gram of fiber is pulled 9,000 m. For example, “220 d”means the fiber having a thickness obtained by pulling one gram of thefiber 9,000/220 =40.9 m. The symbol “f” means “filament” which is a unitfor expressing the number of monofilaments. For example, “70 f” meansthat one multifilament is composed of 70 monofilaments. An expression“kg/5 cm” used for tensile strength is the strength required to pull atest piece of 5 cm width. An expression “parallel” used for the pilestructure means a state that the piles 130 connecting the front meshlayer 110 and the back mesh layer 120 do not cross each other viewedfrom a side, while “cross” means a state that the piles cross each otherviewed from a side.

[0089] As a manner of disposing the piles 130 (pile structure), it canbe classified by a state of the piles 130 connecting the front meshlayer 110 and the back mesh layer 120 viewed from the pile side, and,more concretely, it can be classified, for example, into the followingtypes shown in FIGS. 15. FIG. 15A and FIG. 15B show straight types inwhich the piles 130 are disposed between respective multifilamentscomposing the front mesh layer 110 and respective opposingmultifilaments composing the back mesh layer 120, in which FIG. 15Ashows a straight type knitted in the shape of the FIG. “8”, while FIG.15B shows a straight type simply knitted straight. From FIG. 15C to FIG.15E show cross types in which the piles 130 are knitted in such a mannerthat the piles 130 cross each other at the halfway between respectiveadjacent multifilaments of the front mesh layer 110 and respectiveadjacent multifilaments of the back mesh layer 120. Among them, FIG. 15Cshows a type in which the piles 130 cross in the shape of the FIG. “8”,FIG. 15D shows another cross type in which the piles 130 are knitted asimple cross, and FIG. 15E shows still another cross type in which thepiles 130 cross in groups of two strands together (double cross).

[0090]FIG. 16 to FIG. 20 are views for explaining other embodiments ofthe invention, and any of them is different from the above-describedembodiment in the structure of the base member constituting the lowerlayer. More specifically, a base member 90 shown in FIG. 16 is composedof a reticulate body in which a plurality of longitudinal wires 90 a anda plurality of lateral wires 90 b are perpendicular to each other into asubstantially rectangular lattice form in a plane view. The frontportions of the longitudinal wires 90 a are located on the thirdauxiliary frame member 32, and the rear parts of the longitudinal wires90 a on both sides are engaged with an engaging member 37 a that is abounce preventing means provided on a space keeping frame 37 between theslide frames 24 and 24. Further, one end of the metal spring 41, whoseother end is engaged with the second auxiliary frame member 31, isengaged with the longitudinal wire 90 a on either side. In addition, aportion in the vicinity of the boundary between the longitudinal wire 90a on either side and the lateral wire 90 b disposed at the rear isengaged with one end of a metal spring 45 whose other end is engagedwith the auxiliary frame member 33 located behind the back main frame 22constituting the seat back part. As a result, the base member 90 iselastically supported to stroke in the lateral direction and thevertical direction, thus forming a flat-type elastic member whichabsorbs vibrations transmitted to the first net member 50 and the secondnet member 60 by stroking by imparted vibrations similarly to the basemember 40 composed of the net member of a three-dimensional structure inthe above-described embodiment.

[0091] A base member 91 shown in FIG. 17 is composed of a plate-shapedbody, and its front end is swingably engaged with the third auxiliaryframe member 32 with hook members 91 a. Further, the base member 91 iselastically supported by engaging ends of the metal springs 41, whoseother ends are engaged with the first or second auxiliary frame member30 or 31, with the rim portion of the base member 91 composed of theplate-shaped body, forming a flat-type elastic member. Furthermore,other hook members 91 b are disposed at the rear, and ends of the metalsprings 45, whose other ends are engaged with a wire member 91 c runningbetween the auxiliary frame members 33 constituting the seat back part,are engaged with the hook members 91 b. As a result, as in the case ofthe above explanation, the base member 91 also strokes by vibrations toexhibit a vibration absorbing effect.

[0092] Further, the base member 91 is, as shown in the drawing, fixed tothe space keeping frame 37 with the hook members 91 b as a bouncepreventing means to suppress upward (thrusting the top) displacement,which prevents an occupant from bouncing up by the base member 91. Thewire member 91 c is formed not into a linear form but into a curved formwith projections and depressions in the vertical direction in thedrawing to be imparted a predetermined elastic force, and is disposedbehind the back lining net member 80 to elastically support it.

[0093] A base member 92 shown in FIG. 18 has a reticulate body part 92 cin which longitudinal wires 92 a and lateral wires 92 b are arrangedperpendicular to each other as in the above-described base member 90,and a plate-shaped body part 92 d which supports the back lining netmember 80 and has the same level as that of the lumbar is connected tothe lateral wire 92 b located at the rear. The reticulate body part 92 cis elastically supported by the metal springs 41 with respect to thesecond auxiliary frame members 31. The plate-shaped body part 92 d iselastically supported by a wire member 92 e which is formed into acurved form with projections and depressions in the vertical direction,in the drawing, between the auxiliary frame members 33 constituting theseat back part to be imparted a predetermined elastic force.

[0094] A base member 93 shown in FIG. 19 is composed of a firstreticulate body part 93 c in which longitudinal wires 93 a and lateralwires 93 b are arranged perpendicular to each other and whichcorresponds to the seat cushion part, and a second reticulate body part93 d which is disposed on the seat back side and has the same level asthat of the lumbar. The first reticulate body part 93 c is elasticallysupported on ends of the metal springs 41 whose other ends are engagedwith the second auxiliary frame members 31. The second reticulate bodypart 93 d is elastically supported on ends of the metal springs 45 whoseother ends are engaged with the auxiliary frame members 33 constitutingthe seat back part.

[0095] A base member 94 shown in FIG. 20 is composed of a plate-shapedbody similarly to the base member shown in FIG. 17 but comprises a firstplate-shaped body part 94 a which is disposed corresponding to the seatcushion part and a second plate-shaped body part 94 b which is disposedon the seat back part side and has the same level as that of the lumbar.The rim portion of the first plate-shaped body part 94 a is elasticallysupported on ends of the metal springs 41 whose other ends are engagedwith the first or second auxiliary frame member 30 or 31. The secondplate-shaped body part 94 b is elastically supported on ends of themetal springs 45 whose other ends are engaged with the auxiliary framemembers 33 constituting the seat back part.

[0096] Next, data of various kinds of characteristics are explained,which were measured about the vehicle seat 10 shown in FIG. 1, that is,the vehicle seat 10 including the base member 40 composed of a netmember of a three-dimensional structure, the first net member 50, thesecond net member 60, and the viscoelastic member 70 which is connectedto and supported on the front end part 21 c in the seat cushion part.

[0097]FIG. 21A shows load-deflection curved lines showing staticcharacteristics when a load is applied at a speed of 50 mm/min using acompressed plate in the shape of the haunches. In the drawing, a symbolT denotes the second net member 60, a symbol L the first net member 50,a symbol P the base member 40 composed of the net member of athree-dimensional structure, and a symbol U the viscoelastic member 70connected to and supported on the front end frame member 21 crespectively. As shown in FIG. 21B, “fr-TLPU” shows the seat cushionpart of the vehicle seat 10 of the embodiment 1 including the second netmember 60: the symbol T, the first net member 50: the symbol L, the basemember 40: the symbol P, and the viscoelastic net member 70: the symbolU. The symbols “fr-TLU”, “fr-TPU”, “fr-LP”, “fr-TU”, “fr-L”, and “fr-P”show test examples which were measured without mounting one of themembers constituting the vehicle seat 10 of the embodiment 1. Forexample, “fr-TLU” means a structure having the second net member 60, thefirst net member 50, and the viscoelastic member 70 without the basemember 40. The case of “fr-TPU” means a structure having no first netmember 50.

[0098] As is clear from FIG. 21A, the seat of the embodiment 1 has thelowest amount of deflection (sinking) against the load. In contrast tothis, the cases of the test examples 1 and 2 which do not have eitherthe base member 40 or the first net member 50 have larger amounts ofdeflection as compared with the embodiment. Accordingly, it can beunderstood that the base member 40 and the first net member 50 areeffective in preventing unintended sinking to provide the feeling ofstiffness.

[0099]FIG. 22 is a graph of vibration transmissibility (G/G) obtainedfrom the acceleration (0.3G) of a platform of a vibrator and the valueof an accelerometer held on the head of a test subject where the subjecthaving a weight of 58 kg sit on the vehicle seat and was vibrated bysine waves at a fixed acceleration of 0.3 G by means of the vibrator.The symbols “fr-TLPU” denotes the embodiment 1 similarly to the aboveexplanation, and “fr-TLU” and “fr-TPU” denote the test examples 1 and 2respectively. “Urethane seat (JM74)” shows data of a comparative examplewhich was measured where a test subject having a weight of 74 kg sit onthe previously known urethane seat (comparative example 1). “Urethaneseat (JM82)” shows data of a comparative example which was measuredwhere a test subject having a weight of 82 kg sit on the previouslyknown urethane seat (comparative example 2).

[0100] As is clear from the drawing, any of them is low in resonancefrequency, but the comparative examples 1 and 2 are high in vibrationtransmissibility at the resonance peak to be about 2.9 to about 3 (G/G).In contrast to this, in the case of the embodiment 1 and the testexamples 1 and 2, it is suppressed to be low, about 2.1 to about 2.4(G/G), exhibiting characteristics excellent in vibration absorption.Among them, the embodiment 1 has the lowest vibration transmissibilityat the resonance peak and is thus excellent in vibration absorbingcharacteristics.

[0101]FIG. 23B is a graph showing characteristics to impact vibrationsunder the haunches investigated by measuring the acceleration at theseat cushion part when the seat is vibrated at a frequency of 4 Hz shownin FIG. 23A. The test subject had a weight of 58 kg. “3DNET Seat(Frendee)” shows the data of the above-described embodiment 1. “3DNETSeat (Drift)” shows the data of an aspect in which a flat plate-shapednet member composed of a net member of a three-dimensional structure isemployed as the first net member 50 in place of that in the loop form ofthe embodiment 1 (embodiment 2). “Normal” shows the data of thepreviously known urethane seat (comparative example 3).

[0102] When the upward acceleration shown by a minus value becomes 1.3 Gor more, the seated person usually bounces up. The comparative example 3shows an acceleration of 1 G or more close to the above value, whilethat of the embodiment 1 and the embodiment 2 is 0.8 G or lower, andthey are thus excellent in impact vibration characteristics.

[0103]FIG. 24B shows data obtained by measuring the accelerationsoutputted at the seat back part and the seat cushion part when thevehicle seat of the embodiment 1 is vibrated at a frequency of 4 Hzshown in FIG. 24A. FIG. 25B shows data obtained by measuring theaccelerations outputted at the seat back part and the seat cushion partwhen the vehicle seat composed of the previously known urethane seat isvibrated at a frequency of 4 Hz shown in FIG. 25A (comparative example4). The test subject had a weight of 58 kg in either case.

[0104] From FIG. 24B, it is known that the output at the seat cushionpart is phase delayed by 90 degrees as compared with the output at theseat back part in the case of the embodiment 1. More specifically, inthe case of the embodiment 1, when the seat cushion part sinks down, thetest subject does not greatly sinks toward the seat back part, and whenthe seat cushion part rises up, the subject does not feel a feeling ofpushing-up from the seat back part, movements of the seat cushion partand the seat back part counterbalancing, so that the subject can keep astable seating attitude. In contrast to this, in the case of thecomparative example 4 in FIG. 25, it can be understood that the outputsat the seat cushion part and the seat back part substantiallysynchronize with each other, whereby the subject sinks deep into theseat back part and the seat cushion part, and both of them greatly pushup as a reaction.

[0105]FIG. 26 is a view showing data of the embodiment 1 in FIG. 24through the relation between cycle and acceleration, and FIG. 27 is aview showing data of the comparative example 4 in FIG. 25 through therelation between cycle and acceleration. In both of them, a differentialvalue of the acceleration showing the correlation with sensitivity isobtained, in which the lower this value is, the greater the test subjectfeels a feeling of bounce.

[0106] In the embodiment 1 in FIG. 26, there is only one point in onecycle from zero toward a negative where a feeling of bounce appears, andthe differential value is 1.54. In the case of the comparative example 4in FIG. 27, there are four points in one cycle where a feeling of bounceappears, and the differential values except for one point are more thanthat of the embodiment 1, and it can be understood that a great feelingof bounce happens more often than in the embodiment 1. It should benoted that the figure in FIG. 26 drawn by acceleration and cycle issimilar to the figure drawn by damping characteristics by an oil damper.

[0107]FIG. 28 is a graph showing results of vibration characteristicsinvestigated by vibrating the seat by means of the vibrator based onrandom waves taken from driving at a speed of 80 km/h on ChugokuExpressway and mounting the accelerometer on the head of the testsubject. The subject had a weight of 58 kg. Both of the embodiment 1 andthe embodiment 2 have low resonance peaks as compared with that of thepreviously known urethane seat, and thus it can be understood that theyexhibit excellent vibration absorbing characteristics. Further, since inthe embodiment 1, the resonance peak exists in a region of frequencylower than that of the embodiment 2, the embodiment 1 is slightly betterthan the embodiment 2 in damping property, and the embodiment 2 isslightly better than the embodiment 1 in spring property.

[0108]FIG. 29 is a graph showing results of the same experiment as inthe case of FIG. 28 which was carried out based on random waves takenfrom driving at a speed of 80 km/h on Metropolitan Expressway. The testsubject similarly had a weight of 58 kg. When the embodiment 1 and theembodiment 2 are compared, there is no significant difference. Theirresonance peaks, however, lower when compared with the urethane seat,and thus it can be understood that the seats of the embodiments 1 and 2are excellent in vibration absorbing characteristics.

[0109] As has been described, the vehicle seat of the present inventionis formed in a three-layered structure including the base memberconstituting the lower layer which is supported through the metalsprings, the first net member of a three-dimensional structure which isdisposed above the base member to constitute the middle layer, and thesecond net member of a three-dimensional structure which is disposed tocover the first net member to constitute the upper layer and isstretched with a tension lower than that of the first net member.Accordingly, the base member can stroke by vibrations to absorb them,and the feeling of stiffness can be provided by the first net member.Further, excellent body weight pressure dispersion characteristics,vibration absorbing characteristics, impact absorbing characteristicsand the like which the net member of a three-dimensional structureitself owns are exhibited more effectively than in the previous case,decreasing the feeling of bounce, so that the body of the seated personcan be stably supported. Further, the viscoelastic member is disposed todecrease the feeling of touch with the seat frame, thereby improving thefeeling of supporting the human body.

[0110] While preferred embodiments of the invention have been describedwith a certain degree of particularity with reference to the drawings,obvious modifications and variations are possible in light of the aboveteachings. The scope of the invention is to be determined from theclaims appended thereto.

What is claimed is:
 1. A vehicle seat, comprising: a base memberelastically connected to and supported on any of frame members arrangedseparately in a width direction of a seat frame, through metal springs,to constitute a lower layer; a first net member of a three-dimensionalstructure, in which a front mesh layer and a back mesh layer areconnected by a large number of piles, stretched above said base memberand between the frame members arranged separately in the widthdirection, to constitute a middle layer; and a second net member of athree-dimensional structure, in which a front mesh layer and a back meshlayer are connected by a large number of piles, disposed to cover thetop of said middle layer and stretched with a tension lower than that ofsaid first net member constituting said middle layer, to constitute anupper layer.
 2. The vehicle seat according to claim 1, wherein said basemember is located between frame members constituting a seat cushion partwhich are arranged separately in the width direction of the seat frame,and said metal spring runs between each frame member and each sideportion of said base member.
 3. The vehicle seat according to claim 2,wherein said base member is further elastically supported hung through ametal spring engaged with any of frame members constituting a seat backpart of the seat frame.
 4. The vehicle seat according to any one ofclaims 1, wherein said base member is connected to means for preventingbounce upward.
 5. The vehicle seat according to any one of claims 1,wherein said base member is a substantially flat-type elastic member. 6.The vehicle seat according to claim 5, wherein the substantiallyflat-type elastic member constituting said base member is a net memberof a three-dimensional structure in which a front mesh layer and a backmesh layer are connected by a large number of piles.
 7. The vehicle seataccording to any one of claims 1, wherein said first net memberconstituting said middle layer is stretched in loop form between theframe members arranged separately in the width direction.
 8. The vehicleseat according to claim 1, wherein a viscoelastic member is insertedbetween a part of said first net member constituting said middle layercovering the frame member and said second net member constituting saidupper layer, or between said first net member constituting said middlelayer and the frame member around which said first net member is wound.9. The vehicle seat according to claim 8, wherein said viscoelasticmember is formed into a structure having a plurality of divided blockparts with one or more boundary parts, which are processed thin inthickness, intervening therebetween.
 10. The vehicle seat according toclaim 8, wherein said viscoelastic member is formed includingviscoelastic polyurethane, or is formed including a net member of athree-dimensional structure, in which a front mesh layer and a back meshlayer are connected by a large number of piles, formed into a structurehaving a plurality of divided block parts with one or more boundaryparts, which are processed thin in thickness, intervening therebetween.11. The vehicle seat according to claim 8, wherein said viscoelasticmember is formed including a net member of a three-dimensionalstructure, in which a front mesh layer and a back mesh layer areconnected by a large number of piles, formed into a structure having aplurality of divided block parts with one or more boundary parts, whichare processed thin in thickness, intervening therebetween, andviscoelastic polyurethane which is integrally joined to one face of thenet member of a three-dimensional structure.
 12. The vehicle seataccording to claim 8, wherein said viscoelastic member is formedincluding a net member of a three-dimensional structure, in which afront mesh layer and a back mesh layer are connected by a large numberof piles, formed into a structure having a plurality of divided blockparts with one or more boundary parts, which are processed thin inthickness, intervening therebetween, and an elastic base member toeither face of which the net member of a three-dimensional structure isintegrally joined.
 13. The vehicle seat according to any one of claims 1to 12, wherein a viscoelastic member which is connected to and supportedon any of the frame members forming the seat frame is further disposedat one or both of a front edge portion of the seat cushion part and alumbar supporting part and below said second net member forming saidupper layer.
 14. The vehicle seat according to claim 13, wherein onlyone end of said viscoelastic member disposed on the front edge portionof the seat cushion part is connected to and supported on any of theframe members disposed at the front end of the seat frame for the seatcushion part.